1. Field of the Invention
This invention relates to an engine driven marine vehicle. More specifically, the present invention relates to the water intake for such vehicles. Even more particularly, the present invention relates to a water intake which prevents aerated water and debris from accessing the jet pump.
2. Prior Art
Marine jet drives which propel vessels on water jet propulsion have long been known and used due to certain advantages over the traditional propeller disposed externally of a marine vehicle. Jet propulsion systems are especially attractive under circumstances where a conventional ship's propeller would be exposed to damage by contact with underwater objects. These systems are also attractive because they do not produce appendage drag and do not expose swimmers and animals to risk of injury by the rotating blades of an external propeller. In a typical jet propulsion system, an engine driven impeller, rotating inside an impeller housing, pumps water from below the vessel through an intake duct, then pressurizes and expels the water horizontally behind the vessel through a diffuser housing and a nozzle. A typical example of such a conventional marine jet drive is seen in Oual, U.S. Pat. No. 3,935,833, which shows a pump positioned near the bottom and transom of a marine vessel and which may be driven vertically or horizontally.
The known jet drives, such as that shown in the prior art, have certain drawbacks compared with the conventional external propeller propulsion system. A major drawback is caused by the tendency of the jet intake to become less efficient with the increase in speed due to its fixed shape. More water than is needed by the pump tries to enter the intake as the vessel speed increases, causing added drag. A further drawback is intake water aeration at higher speeds due to the dynamics of air and water at the vessel bottom boundary layer, reducing jet efficiency. Further, there is the tendency of waterborne debris to be caught in the water intake duct causing a reduction in efficiency, sometimes to the point of immobilizing the vessel. Clearing the intake duct is a time consuming process requiring the vessel to be stopped. While conventional jet drives have grid cleaning devices, these devices are not effective, and give a false sense of security. In no case can these cleaning systems free the impeller from debris.
Attempts have been made to address some of these problems. For example, Klepacz et alia, U.S. Pat. No. 3,993,015 shows a elevated water intake trailing edge designed for easier manufacturing. Yet, this edge design does not improve jet efficiency at higher speeds.
Thus, the present invention seeks to provide a marine jet drive propulsion system that overcomes the disadvantages of the known jet drives.